Sleep disturbance and fatigue emerge during the first phase of HIV infection. Given the increased life span of HIV infected patients, and evidence that sleep is necessary for optimal physical and mental health, investigation of the links between HIV and sleep are critically important. Sleep has been implicated as playing a role in brain development and is known to be necessary for optimal immune function, learning, and memory. Therefore, the deterioration of sleep and prominence of fatigue may be particularly deleterious for HIV infected pediatric patients, the majority of whom are first exposed to the virus in utero. There may be significant implications for developmental changes in the brain and sleep may be a high priority target for early intervention. As there is only one published report on pediatric HIV and sleep, the general aim of this study is to use objective assessment techniques (i.e., polysomnography (PSG)) to describe sleep abnormalities in children with HIV. Specific aims include: 1) to describe abnormalities in the organization of sleep stages and to estimate prevalence rates of sleep disorders in HIV infected pediatric patients; and 2) to use objective laboratory based measures of sleep propensity, fatigue and neurocogntive function in HIV infected pediatric patients to describe the daytime disability that has been documented in adult HIV+ patients. The study sample will be 130 children with HIV, and an age matched sample of healthy (seronegative) controls ages 4 to 18 years. All patients will be studied with PSG, Multiples Sleep Latency Tests and performance tests that measure fatigue and sleepiness. Fifty subjects: from each group will also be evaluated with a battery of neurocognitive measures that are sensitive to fatigue and the effects of sleep disruption. Regression analyses and tests of group differences will be used to establish an association between HIV and sleep abnormalities that are linked directly to measures of HIV severity and neurocognitive outcomes. This study is a necessary first step for future studies that will identify specific changes in the brain and in neuroendocrine factors that are the hypothesized mediators of the association between HIV infection, sleep disturbance, and disability. This study will advance clinical science by identifying targets of intervention that will improve children's quality of life, and physical and mental health.